Electronic components of this kind have been demanded to be downsized, to be thinner and to be more sophisticated. On top of that, the market trend of higher speed signaling and digitized devices has required a conductive pattern of the components to be finer and more accurate. Development of finer conductive patterns and thicker films for preventing a wiring resistance from increasing has been advancing in order to meet those requirements, i.e. downsizing, more accuracy, and finer patterns. As a result, the need for forming conductive patterns of higher aspect ratio intensifies.
An electronic component including a conventional conductive pattern is described hereinafter with reference to FIG. 9, which shows a sectional view of the pattern. In FIG. 9, conductive pattern 22 is formed on substrate 21 by printing. Use of electrode material, such as Ag being excellent in conductivity but subject to migration, for pattern 22 usually needs an insulating protective film to cover pattern 22 because of maintaining reliability.
For instance, use of a ceramic-based substrate, e.g. aluminum oxide, as substrate 21 employs insulating protective film 23 made of glass. This film is formed by printing glass-paste, i.e. a mixture of glass powder as a major component, binder and solvent, at a given thickness, then the paste is dried and baked to be the film. Use of compound organic material such as glass-epoxy as substrate 21 employs insulating protective film 23 made of organic material because it is difficult for this substrate 21 to undergo a heat treatment at an excessively high temperature. In this case, film 23 is formed by screen-printing resin paste made mainly of organic material, then the resin undergoes a heat curing process to be film 23. In addition to the foregoing methods, the sputtering method one of thin-film methods can be used for forming SiO2 film as insulating protective film 23.
Electronic components having conductive patterns are disclosed in Japanese Patent Unexamined Publication No. H11-2887799 and ditto H09-237976.
Fine conductive patterns made from electrode material such as Ag is formed on substrate 21 made of the foregoing materials, then insulating protective film 23 is formed by a printing method such as screen-printing. Film 23 thus formed tends to be short of uniformity of film thickness, or tends to produce air bubbles 24 and air gaps 25. As a result, conductive pattern 22 decreases its reliability. Although the foregoing printing method is good at productivity, it is poor at forming film 23 uniform in thickness with accuracy because of viscoelasticity characteristics of the paste.
At the edges of conductive patterns 22, in particular, film 23 becomes thinner or tends to trap air-bubbles 24 in patterns 22. A narrow space between patterns 22 tends to produce air-gaps 25 because the spaces cannot be fully filled with paste.
The thin-film method can form a film uniformly in thickness on a plane section of pattern 22 (parallel with the surface of substrate 21), so that no problem is found. However, it is difficult for the thin-film method to form a film uniformly in thickness on pattern's wall face (vertical with respect to the surface of substrate 21).
In other words, if insulating protective film 23 is formed by the conventional method, it is difficult to prevent the electrode made of Ag from migrating into others. A higher aspect ratio (a ratio of height vs. width) of pattern 22 increases probability of incurring various defects of film 23. As a result, it is difficult to maintain the reliability of withstanding migration. The present invention aims to solve the problems discussed above, and provide highly reliable electronic components having conductive patterns with a high aspect ratio.